Some thoughts, and a few inspection results...
It would seem to be beneficial to differentiate between the the air-oil separator and the crankcase vent valve in this discussion. The CVV is an option on the ASA separator, and to my knowledge, the ASA separator itself is not a root cause of any of the crank seal failures. A coked-up CVV does appear to be involved. There have been broken CVVs as well (I had one).
If a clean belly is the motivation for adding the separator, the CVV does not need to be added, and a catch bottle can be used instead. That's one possible technique at any rate.
My motivation for the CVV addition is performance. It may not be a major enhancement, but this device does have a performance history in other vehicular applications, so I'm giving it a try...my informed choice. As with any performance mod, pros and cons must be weighed, and all measures to mitigate risk should be considered.
When first installed, my CVV did coke up, and the valve itself failed internally. That happened in about 40 hours. Here are a couple pics:
This second pic shows the failed ASA-supplied CVV taken apart, a spare of the same type, and two Napa replacements. The check valve pop-rivet is what appeared to fail, as the diaphragm was just rattling around inside.
I have the ASA tap, and a home-made saddle, as I installed this before ASA offered the saddle. The coking appeared to form in the area of the tap-to-saddle weld. I cleaned it out, and replaced the CVV with the similar Napa part, recommended by Dan H. Here's what the tap looked like cleaned out.
I also filed the inner bore at the weld site, to try to reduce the roughness that the coke appears attracted to (that is speculation). I have added a second valve tee'd in as a safety valve, to mitigate the risk...those seal failure events did indeed get my attention. ASA has also started offering a T valve as a safety as well.
I have about 200 hours on the valve since then, and have inspected it at each oil change, and when the cowl was off for maintenance or pre-race inspection. Intervals have ranged from 20-45 hours. I have not had a recurrence of major coking, or any more valve failures. I do see a bit of coking, still at the area of the weld, but it has been very minor...and easily cleaned. Here is the valve, as it looked upon removal, this past month during condition inspection/oil change (42 hours since last removed and inspected).
I did a little more filing of the bore in hopes of reducing the coking even further. It is very low now, or so it appears.
So the choice to run this piece of equipment (the CVV) brings with it the responsibility to add a safety valve, inspect regularly, or both. There appears to be risk in not doing so, so I am doing both. I've also added a way to measure whether the CVV is creating negative pressure, with a manometer tap...per Dan's suggestion. Will report back with findings when I can test fly...waiting on good weather and days off to coincide. Here's a photo collage of that set-up:
So whether one goes with a breather tube with a whistle slot plumbed overboard, an air-oil separator, with or without a catch bottle, or the full separator/CVV combo, each choice seems to come with inspection, maintenance and care requirements. Complexity does change with each choice, so eyes wide open in the choice.
Good news is we're discussing it, learning, and taking corrective action. For disclosure's sake, ASA has done a little sponsoring of my racing, but that doesn't stop me from having frank conversations with them, or reporting my issues to them...or here on VAF. I think lessons have been learned on all sides.
Not trying to push the product...just still experimenting with it. Hopefully it'll help folks make informed choices. If I've missed any details or other gotchas of this, I'm listening to the operators and mechanics here that have concerns, and trying to install and use this equipment right. Still listening!
Cheers,
Bob
